Revision: 1902
Author: bvwelch
Date: Fri Apr 9 12:24:38 2010
Log: polled version of timer0 interval library
http://code.google.com/p/jallib/source/detail?r=1902
Added:
/trunk/include/peripheral/timer/timer0_poll_interval.jal
=======================================
--- /dev/null
+++ /trunk/include/peripheral/timer/timer0_poll_interval.jal Fri Apr 9
12:24:38 2010
@@ -0,0 +1,150 @@
+-- Title: timer0 poll interval
+-- Author: Joep Suijs, Copyright (C) 2008 Joep Suijs
+-- Adapted-by: Rob Hamerling, William Welch
+-- Compiler: >=2.4m
+--
+-- This file is part of jallib (http://jallib.googlecode.com)
+-- Released under the ZLIB license
(http://www.opensource.org/licenses/zlib-license.html)
+--
+-- Description: Fixed interval support for non-blocking delays, but
without using
+-- an interrupt.
+--
+-- Note: In many (possibly most) cases, you would be wise to choose the ISR
+-- version of this library-- it will be much more accurate.
+--
+-- The setup of this library is straight-forward. First you define the
overflow
+-- rate for the timer. You'll have to make some trade-offs as to accuracy,
frequency
+-- of polling, etc.
+--
+-- >>> const timer0_overflow_rate = 1000 -- 1 kHz overflow rate
+--
+-- Next, you need to specify the number of slots. A slot is used to store
the
+-- end-time of a delay-period so you need one slot for each concurrent
delay.
+--
+-- >>> const DELAY_SLOTS = 2 -- support 2 delays at the same time
+--
+-- Now, include the library and call it's init function:
+--
+-- >>> include timer0_poll_interval
+-- >>> timer0_poll_init() -- init timer0
+--
+-- Now we are ready to use the delay functions. To demonstrate it's use,
we take
+-- two LEDs and let them blink at their own interval:
+--
+-- >> forever loop
+-- >> if (check_delay(0)) then
+-- >> set_delay(0, 409) -- 409 ticks on delay-slot 0
+-- >> led = !led
+-- >> end if
+-- >> if (check_delay(1)) then
+-- >> set_delay(1, 619) -- 619 ticks on delay-slot 1
+-- >> led2 = !led2
+-- >> end if
+-- >> end loop
+--
+
+var word timer0_interval_counter
+var word timer0_countdown[DELAY_SLOTS]
+var byte timer0_load
+
+function interval_counter'get() return word is
+ return timer0_interval_counter
+end function
+
+procedure _timer0_poll() is
+ pragma inline
+
+ if INTCON_TMR0IF == true then
+ tmr0 = timer0_load
+
+ -- counters
+ timer0_interval_counter = timer0_interval_counter + 1
+
+ var byte index
+ for DELAY_SLOTS using index loop
+ if (timer0_countdown[index] != 0) then
+ timer0_countdown[index] = timer0_countdown[index] - 1
+ end if
+ end loop
+
+ -- if user defined wedge procedure, call it.
+ if (defined(timer0_poll_wedge) == true) then
+ timer0_poll_wedge()
+ end if
+
+ INTCON_TMR0IF = off
+ end if
+end procedure
+
+procedure set_delay(byte in slot, word in ticks) is
+
+ if (slot >= DELAY_SLOTS) then return end if
+
+ timer0_countdown[slot] = ticks
+
+end procedure
+
+function check_delay(byte in slot) return bit is
+
+ if (slot >= DELAY_SLOTS) then return true end if
+
+ _timer0_poll()
+
+ if (timer0_countdown[slot] == 0) then
+ return true -- delay passed
+ end if
+
+ return false -- still waiting
+
+end function
+
+procedure timer0_poll_init() is
+
+ const dword timer0_div = (target_clock / 4 / timer0_overflow_rate) - 1
+
+ if (timer0_div > ((256 * 256) - 1)) then
+ pragma error -- requested overflow rate is too low
+
+ elsif (timer0_div > ((128 * 256) - 1)) then
+ T0CON_T0PS = 7 ; prescaler 256
+ timer0_load = 255 - timer0_div / 256
+
+ elsif (timer0_div > ((64 * 256) - 1)) then
+ T0CON_T0PS = 6 ; prescaler 128
+ timer0_load = 255 - timer0_div / 128
+
+ elsif (timer0_div > ((32 * 256) - 1)) then
+ T0CON_T0PS = 5 ; prescaler 64
+ timer0_load = 255 - byte(timer0_div / 64)
+
+ elsif (timer0_div > ((16 * 256) - 1)) then
+ T0CON_T0PS = 4 ; prescaler 32
+ timer0_load = 255 - byte(timer0_div / 32)
+
+ elsif (timer0_div > ((8 * 256) - 1)) then
+ T0CON_T0PS = 3 ; prescaler 16
+ timer0_load = 255 - byte(timer0_div / 16)
+
+ elsif (timer0_div > ((4 * 256) - 1)) then
+ T0CON_T0PS = 2 ; prescaler 8
+ timer0_load = 255 - byte(timer0_div / 8)
+
+ elsif (timer0_div > ((2 * 256) - 1)) then
+ T0CON_T0PS = 1 ; prescaler 4
+ timer0_load = 255 - byte(timer0_div / 4)
+
+ else
+ T0CON_T0PS = 0 ; prescaler 2
+ timer0_load = 255 - timer0_div / 2
+ end if
+
+ T0CON_T0CS = 0 ; internal clock
+ T0CON_PSA = 0 ; assign prescaler to timer0
+
+ var byte i
+ for DELAY_SLOTS using i loop
+ timer0_countdown[i] = 0
+ end loop
+
+end procedure
+
--
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